The limit of blocks that you can create with the script create object on play is 4096 blocks.
The script limit is not well defined and can change depending of how many wires there are, the size of the scripts, along others things.
For more information on this limit read: Is there a limit for scripts?
The limit is 8 connections per output.
A wire split refers to connecting the same wire from an output into 2 or more input ports.
The max size a single object can have is 4x4x4 blocks or 32x32x32 voxels.
The number of blocks in your game plus the number of levels cannot exceed 255. So you can have 254 custom blocks if you only have 1 level. If you have 100 levels, then you can only have 155 blocks. Similarly, if you have over 155 blocks, then you may not have 100 levels. Also, keep in mind that multi-block objects count toward the limit just as if they were separate blocks, so a 2x2x1 multiblock counts as 4 blocks. Unfortunately, there are other mysterious factors affecting this limit so usually the actual limit will likely be a little lower than this.